Sealed methods

A method, indexer, property, or event, on a derived class that is overriding a virtual member of the base class can declare that member as sealed. This negates the virtual aspect of the member for any further derived class. This is accomplished by putting the sealed keyword before the override keyword in the class member declaration

For example:

public class D : C
{
public sealed override void DoWork() { }
}

Here is the more detailed example, in the following example, Z inherits from Y but Z cannot override the virtual function F that is declared in X and sealed in Y.